AUTHOR=Murphy Alexander Peter , Greally Elizabeth , O'Hogain Dara , Blamire Andrew , Caravan Peter , Straub Volker 

TITLE=Use of EP3533-Enhanced Magnetic Resonance Imaging as a Measure of Disease Progression in Skeletal Muscle of mdx Mice

JOURNAL=Frontiers in Neurology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2021.636719

DOI=10.3389/fneur.2021.636719

ISSN=1664-2295

ABSTRACT=<p>As putative treatments are developed for Duchenne muscular dystrophy (DMD), sensitive, non-invasive measures are increasingly important to quantify disease progression. Fibrosis is one of the histological hallmarks of muscular dystrophy and has been directly linked to prognosis. EP3533 is a novel contrast agent with an affinity to collagen 1 that has demonstrated a significant and high correlation to <italic>ex vivo</italic> fibrosis quantification. Halofuginone is an established anti-fibrotic compound shown to reduce collagen skeletal muscle fibrosis in murine models of DMD. This experiment explored whether EP3533 could be used to detect signal change in skeletal muscle of <italic>mdx</italic> mice before and after a 12 week course of halofuginone compared to controls. Four age-matched groups of treated and untreated mice were evaluated: 2 groups of <italic>mdx</italic> (<italic>n</italic> = 8 and <italic>n</italic> = 13, respectively), and 2 groups of BL10 mice (<italic>n</italic> = 5 and <italic>n</italic> = 3, respectively). Treated mice received an intraperitoneal injection with halofuginone three times per week for 12 weeks, with the remaining mice being given vehicle. Both <italic>mdx</italic> groups and the untreated BL10 were scanned at baseline, then all groups were scanned on week 13. All subjects were scanned using a 7T Varian scanner before and after administration of EP3533 using a T1 mapping technique. Mice underwent grip testing in week 13 prior to dissection. Skeletal muscle was used for Masson's trichrome quantification, hydroxyproline assay, and immunofluorescent antibody staining. Untreated <italic>mdx</italic> mice demonstrated a significant increase in R1 signal from pre- to post-treatment scan in three out of four muscles (gastrocnemius <italic>p</italic> = 0.04, hamstrings <italic>p</italic> = 0.009, and tibialis anterior <italic>p</italic> = 0.01), which was not seen in either the treated <italic>mdx</italic> or the BL10 groups. Histological quantification of fibrosis also demonstrated significantly higher levels in the untreated <italic>mdx</italic> mice with significant correlation seen between histology and EP3533 signal change. Forelimb weight adjusted-grip strength was significantly lower in the untreated <italic>mdx</italic> group, compared to the treated group. EP3533 can be used over time as an outcome measure to quantify treatment effect of an established anti-fibrotic drug. Further studies are needed to evaluate the use of this contrast agent in humans.</p>